This invention relates generally to gas pressure diaphragm regulator valves and particularly to liquified petroleum (LP) pressure regulator valve for residential use.
Gas pressure diaphragm type regulator valves are well-known in the art. In such valves, a valve disk and a mating seat assembly are positioned intermediate to an upstream and a downstream portion of a flowpath for controlling downstream pressure and gas flow by varying the valve opening, that is, the amount by which the valve disk is displaced from its associated valve seat. Gas pressure and flow regulation are achieved by modulating the valve opening to maintain the required downstream pressure while delivering the quantity of gas demanded by the load. The popular, low cost, single stage regulator valve includes a diaphragm that acts as both the measuring and the actuation device with the downstream pressure being applied to one side of the diaphragm against the force of an opposed, adjustable regulator spring. The spring force initially holds the diaphragm and the attached stem linkage mechanism in such a position so as to have retracted the valve disk from the valve seat. As upstream pressure is introduced, gas flow occurs through the seat to the disk opening and into the downstream side of the device. The downstream pressure force is applied against the diaphragm and enables the diaphragm to overcome the opposing regulator spring force, thereby moving the stem linkage and the valve disk to a position closer to the valve seat. In this manner, the adjustment of the regulator spring loading determines the downstream control pressure as a force equilibrium is achieved between the loading force of the spring and the force on the diaphragm from the downstream pressure. The linkage mechanism provides a mechanical advantage which enables a small diaphragm, actuated by very low downstream control pressures, to close the valve disk against the valve seat despite the relatively high pressure acting to push the disk open.
All single or first stage regulator valves experience "droop" in their pressure flow characteristic because the regulating spring changes in length and the effective area of the diaphragm changes as the diaphragm moves. These effects lower the downstream control pressure with flow increases. "Velocity boosting" is often used to apply a slightly lower pressure than the controlled downstream pressure to the diaphragm, thereby producing a larger valve opening and enabling greater gas flow.
It will be appreciated that in domestic gas service, the downstream pressure must be maintained at an extremely low level, on the order of 7 to 11 inches (approximately 18 to 28 centimeters) of water column pressure for natural gas and LP gas service, respectively, whereas the inlet or upstream pressure may be on the order of 60 psi (4.22 Kg per square centimeter) or more. Good pressure relief operation is required to preclude potentially serious over pressure conditions in the downstream system as well as to minimize annoying (and potentially dangerous) extinguishing of pilot lights in domestic appliances. However, the demands on gas pressure regulators, for domestic use in particular, are such that design compromises are required in the simple mechanical devices. For example, friction and hysteresis or backlash, inherent in linkage mechanisms, detract from the consistency of regulator performance. As mentioned, the spring effect and the diaphragm effect combine to cause output pressure droop. This droop will be overcome only at certain inlet pressures or across limited flow ranges by imprecise velocity boosting techniques The fixed mechanical advantage linkage mechanisms do nothing to overcome droop. In many current examples of the art, the relief valve is contained in an actuator housing which is separated from the body that houses the valve seat, forcing overpressured downstream gas to flow through restricting passages before reaching the relief valve for venting.
The gas pressure regulator valve described and claimed in U.S. Pat. No. 4,842,013, dated 6/27/89, entitled "Droop Compensated Direct Acting Pressure Regulator," in the names of D. D. Rice and M. E. Hood, and assigned to the assignee of the present invention, utilizes a combination of a characterized cam stem and an orifice tube (which is a valve seat with an integral boost tube). The characterized or contoured cam stem has a cam profile that is directly operable by the regulator spring and diaphragm for effecting rectilinear movement of a valve disk into and out of engagement with a valve seat at a nonlinear rate, without the intervention of any linkage mechanism. The cam stem provides a high mechanical advantage when required to close the valve disk against the seat, yet exhibits a low mechanical advantage to achieve rapid, nonlinear opening of the valve disk to mechanically induce a boost effect and maintain the desired downstream control pressure in all flow situations. The orifice tube aids in the uniformity of regulation by inducing a flow activated boost. Its configuration determines the space between the end of the tube and the valve outlet which in turn controls aspiration of the diaphragm cavity, which is the downstream pressure measuring element of the regulator. The direct acting pressure regulator valve is suitable for either natural gas or L/P gas service use by simply changing the predetermined, adjustable relief valve spring and regulator spring loads.
A removable boost end cap may also be provided for the orifice tube. The boost end cap has an orifice that is smaller in diameter than the diameter of the orifice tube and larger in diameter than the diameter of the valve seat, thus providing a design controlled boost effect. The boost end caps are manufactured with different size orifices for use with orifice tubes with corresponding size valve seats to enable a common valve design to have its individual operating characteristics tailored to different environmental conditions. The valve of the present invention is especially designed for LP gas residential service where the inlet pressure is higher than it is for natural gas. The invention is however also applicable to other types of valves and service.
Under certain pressure and flow conditions, the regulating mechanism might experience lower spring seat harmonic motion or vibration that could be annoying. In accordance with the invention, a dampener is placed on the lower spring seat which is fabricated in the form of a cylindrical insert. The dampener is an 0 ring that frictionally engages the interior of the spring chamber for dampening vibrations of the movable spring seat insert. The cam stem has also been changed to provide positive upper and lower stops to preclude lock up and pull out of the stem under abnormal operating conditions.